FFmpeg: libavcodec/mss1.c Source File

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libavcodec

mss1.c

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1 /*

2 * Microsoft Screen 1 (aka Windows Media Video V7 Screen) decoder

4 *

5 * This file is part of FFmpeg.

6 *

7 * FFmpeg is free software; you can redistribute it and/or

8 * modify it under the terms of the GNU Lesser General Public

9 * License as published by the Free Software Foundation; either

10 * version 2.1 of the License, or (at your option) any later version.

11 *

12 * FFmpeg is distributed in the hope that it will be useful,

13 * but WITHOUT ANY WARRANTY; without even the implied warranty of

14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

15 * Lesser General Public License for more details.

16 *

17 * You should have received a copy of the GNU Lesser General Public

18 * License along with FFmpeg; if not, write to the Free Software

19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

20 */

22 /**

23 * @file

24 * Microsoft Screen 1 (aka Windows Media Video V7 Screen) decoder

25 */

27 #include "avcodec.h"

28 #include "internal.h"

29 #include "mss12.h"

31 typedef struct MSS1Context {

32 MSS12Context ctx;

33 AVFrame *pic;

34 SliceContext sc;

35 } MSS1Context;

37 static void arith_normalise(ArithCoder *c)

38 {

39 for (;;) {

40 if (c->high >= 0x8000) {

41 if (c->low < 0x8000) {

42 if (c->low >= 0x4000 && c->high < 0xC000) {

43 c->value -= 0x4000;

44 c->low -= 0x4000;

45 c->high -= 0x4000;

46 } else {

47 return;

48 }

49 } else {

50 c->value -= 0x8000;

51 c->low -= 0x8000;

52 c->high -= 0x8000;

53 }

54 }

55 c->value <<= 1;

56 c->low <<= 1;

57 c->high <<= 1;

58 c->high |= 1;

59 c->value |= get_bits1(c->gbc.gb);

60 }

61 }

63 ARITH_GET_BIT(arith)

65 static int arith_get_bits(ArithCoder *c, int bits)

66 {

67 int range = c->high - c->low + 1;

68 int val = (((c->value - c->low + 1) << bits) - 1) / range;

69 int prob = range * val;

71 c->high = ((prob + range) >> bits) + c->low - 1;

72 c->low += prob >> bits;

74 arith_normalise(c);

76 return val;

77 }

79 static int arith_get_number(ArithCoder *c, int mod_val)

80 {

81 int range = c->high - c->low + 1;

82 int val = ((c->value - c->low + 1) * mod_val - 1) / range;

83 int prob = range * val;

85 c->high = (prob + range) / mod_val + c->low - 1;

86 c->low += prob / mod_val;

88 arith_normalise(c);

90 return val;

91 }

93 static int arith_get_prob(ArithCoder *c, int16_t *probs)

94 {

95 int range = c->high - c->low + 1;

96 int val = ((c->value - c->low + 1) * probs[0] - 1) / range;

97 int sym = 1;

99 while (probs[sym] > val)

100 sym++;

101

102 c->high = range * probs[sym - 1] / probs[0] + c->low - 1;

103 c->low += range * probs[sym] / probs[0];

104

105 return sym;

106 }

107

108 ARITH_GET_MODEL_SYM(arith)

109

110 static void arith_init(ArithCoder *c, GetBitContext *gb)

111 {

112 c->low = 0;

113 c->high = 0xFFFF;

114 c->value = get_bits(gb, 16);

115 c->gbc.gb = gb;

116 c->get_model_sym = arith_get_model_sym;

117 c->get_number = arith_get_number;

118 }

119

120 static int decode_pal(MSS12Context *ctx, ArithCoder *acoder)

121 {

122 int i, ncol, r, g, b;

123 uint32_t *pal = ctx->pal + 256 - ctx->free_colours;

124

125 if (!ctx->free_colours)

126 return 0;

127

128 ncol = arith_get_number(acoder, ctx->free_colours + 1);

129 for (i = 0; i < ncol; i++) {

130 r = arith_get_bits(acoder, 8);

131 g = arith_get_bits(acoder, 8);

132 b = arith_get_bits(acoder, 8);

133 *pal++ = (0xFFU << 24) | (r << 16) | (g << 8) | b;

134 }

135

136 return !!ncol;

137 }

138

139 static int mss1_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,

140 AVPacket *avpkt)

141 {

142 MSS1Context *ctx = avctx->priv_data;

143 MSS12Context *c = &ctx->ctx;

144 GetBitContext gb;

145 ArithCoder acoder;

146 int pal_changed = 0;

147 int ret;

148

149 if ((ret = init_get_bits8(&gb, avpkt->data, avpkt->size)) < 0)

150 return ret;

151

152 arith_init(&acoder, &gb);

153

154 if ((ret = ff_reget_buffer(avctx, ctx->pic)) < 0)

155 return ret;

156

157 c->pal_pic = ctx->pic->data[0] + ctx->pic->linesize[0] * (avctx->height - 1);

158 c->pal_stride = -ctx->pic->linesize[0];

159 c->keyframe = !arith_get_bit(&acoder);

160 if (c->keyframe) {

161 c->corrupted = 0;

162 ff_mss12_slicecontext_reset(&ctx->sc);

163 pal_changed = decode_pal(c, &acoder);

164 ctx->pic->key_frame = 1;

165 ctx->pic->pict_type = AV_PICTURE_TYPE_I;

166 } else {

167 if (c->corrupted)

168 return AVERROR_INVALIDDATA;

169 ctx->pic->key_frame = 0;

170 ctx->pic->pict_type = AV_PICTURE_TYPE_P;

171 }

172 c->corrupted = ff_mss12_decode_rect(&ctx->sc, &acoder, 0, 0,

173 avctx->width, avctx->height);

174 if (c->corrupted)

175 return AVERROR_INVALIDDATA;

176 memcpy(ctx->pic->data[1], c->pal, AVPALETTE_SIZE);

177 ctx->pic->palette_has_changed = pal_changed;

178

179 if ((ret = av_frame_ref(data, ctx->pic)) < 0)

180 return ret;

181

182 *got_frame = 1;

183

184 /* always report that the buffer was completely consumed */

185 return avpkt->size;

186 }

187

188 static av_cold int mss1_decode_init(AVCodecContext *avctx)

189 {

190 MSS1Context * const c = avctx->priv_data;

191 int ret;

192

193 c->ctx.avctx = avctx;

194

195 c->pic = av_frame_alloc();

196 if (!c->pic)

197 return AVERROR(ENOMEM);

198

199 ret = ff_mss12_decode_init(&c->ctx, 0, &c->sc, NULL);

200 if (ret < 0)

201 av_frame_free(&c->pic);

202

203 avctx->pix_fmt = AV_PIX_FMT_PAL8;

204

205 return ret;

206 }

207

208 static av_cold int mss1_decode_end(AVCodecContext *avctx)

209 {

210 MSS1Context * const ctx = avctx->priv_data;

211

212 av_frame_free(&ctx->pic);

213 ff_mss12_decode_end(&ctx->ctx);

214

215 return 0;

216 }

217

218 AVCodec ff_mss1_decoder = {

219 .name = "mss1",

220 .long_name = NULL_IF_CONFIG_SMALL("MS Screen 1"),

221 .type = AVMEDIA_TYPE_VIDEO,

222 .id = AV_CODEC_ID_MSS1,

223 .priv_data_size = sizeof(MSS1Context),

224 .init = mss1_decode_init,

225 .close = mss1_decode_end,

226 .decode = mss1_decode_frame,

227 .capabilities = CODEC_CAP_DR1,

228 };

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